1. Field of the Invention
The present invention relates to an image capturing apparatus having an object detection function.
2. Description of the Related Art
In conventional focus adjustment control of image capturing apparatuses such as a video camera, the TV-AF method is the mainstream. According to this method, a focus signal representing sharpness (contrast) is detected from image signals obtained by an image sensor, and the focus lens position is controlled to maximize the focus signal.
For example, Japanese Patent Laid-Open No. 2006-227080 proposes an arrangement in which a face region is detected as a predetermined target object from an image, an AF (Auto Focus) area is set to contain the detected face region, and focus detection is done. When a face region is detected, an image capturing apparatus having this arrangement performs AF control using a focus signal obtained from the face region, and when no face region is detected, executes it using a focus signal obtained from the entire frame.
When a predetermined target object is detected from a moving image, like a video camera, it is difficult to keep stably detecting the target object because the target object moves or changes the direction. The image capturing apparatus having the arrangement disclosed in Japanese Patent Laid-Open No. 2006-227080 often switches between a state in which AF is done using a focus signal obtained from the face region and a state in which AF is done using a focus signal obtained from the entire frame. The image changes frequently, bothering the user.
As a measure to solve a similar problem, Japanese Patent Laid-Open No. 2007-68147 proposes an image capturing apparatus which, even if a target object which has been detected is lost, keeps displaying an object frame displayed over the target object for a predetermined holding time. When a target object is lost for only a short time, the image capturing apparatus keeps displaying the object frame representing that the target object is displayed. This can prevent the object frame from frequently appearing and vanishing, and thus can reduce an annoying display on the frame. This arrangement can be applied to the TV-AF method to suppress frequent switching of the target position of the focus lens. That is, even if a face region which has been detected is lost, AF control is executed for a predetermined holding time using a focus signal obtained from the region where the face region has been detected.
However, there is a challenge in how to set a predetermined holding time for holding a control state before losing a target object when the target object is lost. More specifically, when the holding time is set long, it can be suppressed to frequently switch the target position of the focus lens. However, even if the target object moves out of the frame, the control does not switch quickly, failing in appropriate AF control for a new object. In contrast, when the holding time is set short, AF control can quickly track a new object upon a change of the object. However, even when the target object vanishes only temporarily, the target position of the focus lens is switched, as described above, and the image changes annoyingly.
This is not limited to AF control. The same problem arises when a predetermined target object is detected from an image to perform image correction processes such as AE (Auto Exposure) control, WB (White Balance) control, luminance signal correction, and noise reduction.